Absorbing nonwoven materials are often used for wiping spills and leakages of all kinds in industrial, service, office and home locations. The basic synthetic plastic components normally are hydrophobic and will absorb oil, fat and grease, and also to some degree water by capillary force. To reach a higher water absorption level, cellulosic pulp can be added. There are many demands put on nonwoven materials made for wiping purposes. An ideal wiper should be strong, absorbent, abrasion resistant and exhibit low linting. To replace textile wipers, which is still a major part of the market, they should further be soft and have a textile touch.
Hydroentangling or spunlacing is a technique introduced during the 1970'ies, see e.g. CA patent no. 841 938. The method involves forming a fibre web which is either drylaid or wetlaid, after which the fibres are entangled by means of very fine water jets under high pressure. Several rows of water jets are directed against the fibre web which is supported by a movable fabric. The entangled fibre web is then dried. The fibres that are used in the material can be synthetic or regenerated staple fibres, e.g. polyester, polyamide, polypropylene, rayon or the like, pulp fibres or mixtures of pulp fibres and staple fibres. Spunlace materials can be produced with high quality to a reasonable cost and have a high absorption capacity. They can e.g. be used as wiping material for household or industrial use, as disposable materials in medical care and for hygiene purposes etc.
From U.S. Pat. No. 6,706,652 it is known to make a nonwoven cleaning cloth of continuous multicomponent filaments which are laid down and optionally pre-bonded. The filaments are then split and bonded, preferably by high-pressure fluid jets to form a cleaning cloth with a very uniform thickness and isotropic fibre distribution. The cloth has no tendency to delaminate.
Such a nonwoven consisting only of filaments will normally be rather flat and have a low bulk, especially for lower basis weights.
From EP-A-0 308 320 it is known to bring together a prebonded web of continuous filaments with a separately prebonded wetlaid fibrous web containing pulp fibres and staple fibres and hydroentangle together the separately formed webs to a laminate.
In such a laminate the fibres or filaments from one of the webs will not be integrated with filaments or fibres from the other web since the fibres or filaments already prior to the hydroentangling are bonded to each other in each separate prebonded web and only have a very limited mobility. The laminate will show a marked two-sidedness. The staple fibres used have a preferred length of 12 to 19 mm, but could be in the range from 9.5 mm to 51 mm.
In WO 2001/88247 is disclosed a method of making a nonwoven that can be three-dimensionally patterned. A web of splittable filaments or carded splittable bicomponent staple fibres is preentangled and then transferred to a patterning drum for final hydroentangling, where the splittable filaments or fibres will be split into finer fibrils which are more pliable and can adjust very well to the patterning drum, such that a material with a very pronounced three-dimensional pattern can be achieved.
One problem is clearly seen with hydroentangled materials where different fibres are to be mixed with each other—they will very often be markedly two-sided, i.e. it can clearly be discerned a difference between the side of the material facing the fabric and the side of the material facing the water jets in the entangling step. In some cases this has been used as a favourable feature, but in most cases it is seen as a disadvantage. When two separate layers are combined and fed into an entangling process, normally this process step cannot thoroughly mix the layers, but the layers will still be discernible, albeit bonded to each other. With pulp in the composite there will be a pulp-rich side and a pulp-poor side, which will result in differing properties of the two sides. Also if a filament web and a staple fibres web are mixed, there will be a side rich in staple fibres and a side rich in filaments. This is pronounced when spunlaid filaments are used as they tend to form a flat two-dimensional layer when created, which will mix poorly. Some producers have tried to first add a covering layer and entangle from one side and then turn the web around and add another covering layer and entangle from the other side, but most of the fibre-moving occurs very early in the entangling process, and this more complicated process does not fully solve the problem.
The splitting of splittable bicomponent staple fibres is normally a very energy-intensive operation, as the fibre segments before they are treated by a card need to be strong enough to hold together during the fibre bale opening and the web preparation of the fibres, otherwise the amount of ‘fibres’ to be handled by the card would be multiplied and the process load on the card would be too high.
Another problem when using a web consisting only of filaments in a hydroentangled nonwoven is that there will be few free fibre ends, as the filaments in principle are without ends, and only staple and pulp fibres can contribute with free ends. Especially polymer fibre ends are what will give the material a textile feeling by their softening effect. In some hydroentangled composites pulp has been added because of its water absorption capacity, which will also add a lot of fibre ends, but as the pulp fibres engage in hydrogen bonds they will not contribute to a soft textile feeling; instead they will make the resulting material feel much harsher. Thus to get a soft textile-feeling material it is important to have a high percentage of textile, i.e. synthetic, staple fibres in a hydroentangled nonwoven material.